The present invention relates to an improvement in an eccentric facing unit or head in which a tool shaft or a facing tool holding shaft is disposed eccentrically with respect to a spindle.
This kind of eccentric facing unit is well known, wherein the tool shaft relatively rotates with respect to the spindle during rotation thereof so as to change a radial distance or radial displacement stroke of a cutting edge (cutting blade) of a facing tool from the axis of the spindle to thereby carry out the facing.
The well known eccentric facing unit is advantageously comprised of only a rotary shaft system, which is easy to attain an ideal balance or balance in two axially spaced planes because all of centrifugal forces can be received or supported by bearings not so as to be transmitted to a driving system and the like of the unit.
However, this eccentric facing unit has a disadvantage in a change or fluctuation of a rake angle (and a cutting angle) of the cutting edge which results in changes of the cutting resistance, the cutting temperature, the surface roughness and the like. Further, in the eccentric facing unit, the larger the radial displacement stroke of the cutting edge becomes, the more the rake angle thereof changes. Accordingly the use of this eccentric facing unit is limited to the facing of a small radial displacement stroke of the cutting edge in which the change of the rake angle is extremely small.
It is therefore an object of the present invention to provide an eccentric facing unit comprising only a rotary shaft system, which has a constant rake angle of a cutting edge.
An eccentric facing unit according to the present invention includes a tool driving shaft, a tool-shaft supporting shaft and a tool shaft. The tool driving shaft is concentrically disposed in a spindle and is relatively rotating with respect to the spindle during rotation thereof. The tool-shaft supporting shaft is eccentrically disposed in the spindle and is connected with the tool driving shaft through a geared transmission so as to rotate at speed twice or two times faster than that of the tool driving shaft. The tool shaft integrally rotating with the tool driving shaft at the same speed, is eccentrically disposed in the tool-shaft supporting shaft in an eccentricity equal to that of the tool-shaft supporting shaft with respect to the spindle.
The basic concept or principle of the eccentric facing unit according to the present invention is schematically shown in FIG. 1. Point P corresponding to the axis of the tool-shaft supporting shaft is disposed apart from point O corresponding to the axis of the spindle and point Q corresponding to the axis of the tool shaft is disposed apart from point P at a equal distance respectively, and point R apart from point Q corresponds to a tip of cutting edge of a facing tool, and when segment PQ belonging to the tool-shaft supporting shaft rotates an angle of xcex8 around point P so that point Q moves to point Qxe2x80x2 through the tool driving shaft, segment QR belonging to the facing tool rotates an angle of xcex8/2 around point Q so as to extend as segment Qxe2x80x2Rxe2x80x2 through the tool driving shaft.
In such a construction, the extension of segment Qxe2x80x2Rxe2x80x2 always passes through point O, that is, the face rectangular to the cutting direction of the cutting edge always passes through the axis of the spindle, thereby keeping the rake angle of the cutting edge permanently constant.
The tool shaft is preferably connected with the tool driving shaft through an Oldham""s shaft coupling. This Oldham""s shaft coupling makes possible the accurate compensation of the working errors on eccentricities of the tool-shaft supporting shaft and the tool shaft, in other words, the working errors on distances from the axis of the spindle to that of the tool-shaft supporting shaft and from the axis of the tool-shaft supporting shaft to that of the tool shaft.
As mentioned above, the eccentric facing unit of the invention keeps the rake angle of the cutting edge always constant, so that the stable facing, in which the cutting resistance, the cutting temperature, the surface roughness or the like are substantially constant, is performable.
The eccentric facing unit can attain an ideal balance, that is, balance in two axially spaced planes because of being comprised of only a rotary shaft system.
Furthermore, the eccentric facing unit is simple in construction and can be manufactured at low cost, and can also be incorporated into an automatic tool changer in machining center to apply for the high speed boring and recessing work.
Other objects, features and advantages of the invention will become more apparent from the following description taken in connection with the accompanying drawings.